1. Field of the Invention
The invention concerns a blind rivet nut with a shank comprising a thread and a deformation zone, with a set head having a larger outside diameter than the shank. Further, the invention concerns a fastening unit with a blind rivet nut of this kind.
2. Description of the Related Art
Blind rivet nuts have been tried and tested for fastening tasks in which a screw connection is required in thin-walled materials, for example, sheet metals, in which normally no thread can be cut. The blind rivet nut is in this case fixed in the sheet metal like a blind rivet and, after fastening thereof, provides a thread for a screw connection which thread has sufficient axial length. The blind rivet nut is set normally by screwing a threaded mandrel into the thread of the shank and placing the blind rivet nut in the preformed hole of the sheet metal. By pulling on the threaded mandrel, the deformation zone is deformed and expanded, with the result that a closing head is produced on the side of the sheet metal opposite the set head. The closing head anchors, together with the set head, the blind rivet nut in the sheet metal. Subsequently, the threaded mandrel is unscrewed. The blind rivet nut is then available as a receptacle for a fastening bolt.
A blind rivet nut of the kind mentioned hereinbefore is known from U.S. Pat. No. 5,259,714 A, which shows the fastening unit together with the bolt. The set head of the nut is made very large and provided with recesses, whereby the nut is to be prevented from also turning when the bolt is tightened. With the blind rivet nut it is possible to fasten one component to another component. A drawback with this solution is that the torque for tightening the bolts is transmitted to the component to be fastened. Hence, the component to be fastened may possibly turn as well, leading to consequential damage. Moreover, the part to be fastened is no longer releasable.
EP 0 494 747 B1 shows a blind rivet nut with preassembled bolt. The bolt head is at a predefined distance from the set head of the blind rivet nut. Hence, the bolt can be used to set the nut. To fasten a workpiece to a component, however, the bolt must first be unscrewed and then screwed back in together with the workpiece.
GB 2 310 904 A shows a blind rivet nut in which the shank comprises two deformation zones with different deformation properties. Thus, it is possible to connect two sheet metals to each other successively in stages. Then a further workpiece can be fastened to the combined sheet metals by means of a bolt. However, three operations are required to fasten the actual workpiece.
EP 0 936 362 A2 shows a blind rivet nut with a shank which is stepped on the outside and has a greater wall thickness adjoining the set head. As this region has an axial length which is greater than the thickness of the sheet metal, it is possible to fasten the nut in the sheet metal loosely or rotatably. The workpiece is screwed on after the operation of setting the blind rivet nut.
GB 2 300 031 A shows a combination of blind rivet nut, expanding portion, and bolt. With this combination, a workpiece can be movably and releasably fastened to a sheet metal in several steps. However, the combination consists of three parts. A pulling operation followed by a screwing operation is required for fastening.
With the known blind rivet nuts, several operations are therefore always required in order to fasten a component to a sheet metal or to a comparable plate-like material, namely screwing a pull mandrel into the blind rivet nut, forming the closing head on the reverse side of the sheet metal, unscrewing the pull mandrel and screwing the fastening bolt in. Alternatively, the blind rivet nut can also be used to connect two components to each other permanently after the fashion of a rivet. But in this case the connection is not releasable.